The present invention relates to a valve lock for locking a valve spindle in a selected position relative to a valve body, and to an adapter for interengaging for example a valve lock assembly and a valve spindle.
Valve locks are required to provide a means for locking a rotatable valve spindle in a pre-determined position. For example, in industrial installations in which potentially hazardous fluids are pumped through process equipment it is often necessary to secure a series of valves in a particular configuration. Valves are locked both to prevent unauthorised operation and, where a series of valves are interlocked, to prevent the sequential operation of a series of valves in a potentially dangerous manner. In an interlocked system, there may be for example three valves which must be opened in a predetermined sequence. In such a system, it is known to provide a key on the first valve in the sequence which can only be removed once that valve has been opened, that key then being used to release a second valve to enable that second valve to be opened, and a further key mounted on the second valve then being released to enable the third valve to be opened. Such key-operated mechanisms are widely used in the process control industry, and one such mechanism is described in British patent specification number 2292207.
Where a valve lock has a captive key that can only be removed once the valve has been fully closed, the mechanism requires a valve spindle position indicating mechanism which prevents key removal until the valve spindle has been rotated to a pre-determined axial and rotational position. Su mechanisms are often referred to as xe2x80x9ccountersxe2x80x9d as in effect it is necessary to pre-set the position of the spindle at which the key is to be released, to count rotations of the spindle away from that initial position, and then to count rotations of the spindle back to the initial position. Thus rotation of the valve spindle is tracked by the counting mechanism such that when the valve spindle is returned to its initial position the valve position counting mechanism indicates that this is the case and releases the key.
One problem with the valve position indicator systems of known valve locks is that of setting the xe2x80x9cinitialxe2x80x9d position during first installation. The mechanisms are delivered with the counters engaged with the other parts of the mechanism. Once installed on a valve, the counters must be reset so as to correctly indicate valve spindle positions at which keys are to be released. Generally this is achieved by removing a casing cover and manually resetting counter components, for example by rotating sprockets using a tool such as a screwdriver. It is highly undesirable to have to rely upon such manual intervention in the normal operation of the mechanism.
Another problem with the valve position indicator systems of known valve locks is that once they have been set, during installation, they are very difficult to reset. This is a severe problem in circumstances where over time the valve spindle position corresponding to the valve being fully closed changes. Such changes often occur as the result of compression over time of valve seals. For example, in a new installation, when the valve is fully closed by applying an appropriate torque to a hand wheel actuator, the valve spindle rotates until resilient valve seals are compressed to an extent sufficient to resist that applied torque. Over time, as the valve seals age and are subjected to repeated compression and relaxation, the same applied torque could result in the valve spindle being turned several times beyond the initial xe2x80x9cfully closedxe2x80x9d position Thus if the locking mechanism is not reset, a valve which is locked in the xe2x80x9cfully closedxe2x80x9d condition may in fact be several turns away from being fully closed. Potentially dangerous leakage can therefore occur through a valve which is nominally fully closed.
In a conventional valve lock, the valve spindle is interengaged with a hub of the lock mechanism such that rotation of the hub is directly coupled to the spindle. In the known devices, this interengagement is achieved by fitting a customised body between the spindle and the hub, the body defining a bore the cross-section of which is machined to match the cross-section of the valve spindle and having an outer periphery defining two slots which receive mating ribs on the hub. Such an arrangement works perfectly satisfactorily but raises two problems. Firstly, the interengaging body has to be designed to fit a particular spindle cross-section and therefore the installer has to know in advance of installation the detailed geometry of the valve spindle. As a result a detailed specification of the valve structure has to be prepared for the installer and valve locks cannot be reliably fitted without such advance information. Secondly, given that it is often the case that the valve lock must be mounted in a pre-determined orientation on the valve body, and must be interengaged with the valve spindle once the valve has been fully closed, it is sometimes necessary to partially open the valve by rotating the spindle back from its fully closed position until the spindle is in a position in which it can be inserted in the bore in the interengaging body mounted in the hub. It would be highly advantageous if a device could be provided which would enable a fitter to install a valve lock on a valve spindle without prior knowledge of the spindle geometry and without significant constraint on the relative orientation of the spindle and the valve body when the interengagement is established.
It is an object of the present invention to obviate or mitigate one or more of the problems outlined above.
According to the present invention, there is provided a valve lock for locking a valve spindle in a selected position relative to a valve body, comprising a housing which in use is mounted on the valve body, a spindle engaging member which rotates with the valve spindle relative to the housing, a latch which is actuable by a key to assume a latched condition in which rotation of the spindle engaging member relative to the housing is permitted in one direction but prevented in the other direction, and a spindle position indicator coupled by a transmission to the spindle engaging member so as to be displaced as a result of rotation of the spindle, wherein the spindle position indicator prevents actuation of the latch by the key except when the spindle position indicator is in a predetermined orientation, the spindle position indicator is locked in the predetermined orientation when the latch has been actuated by the key, and the transmission incorporates a slip clutch which enables rotation of the spindle engaging member in the said one direction if the spindle position indicator is locked in the pre-determined orientation and sufficient torque is applied to the spindle engaging member, whereby the selected position can be reset.
With valve locks on a accordance with the invention, initial setting of the spindle position indicator upon installation can be readily achieved by locking the indicator and then relying upon the ratchet-like latch to enable movement of the spindle to a desired xe2x80x9csetxe2x80x9d position. Equally, if after prolonged use a user of such a valve lock turns the valve spindle to an extreme position and discovers that the valve lock is not operable in that extreme position, the valve can simply be rotated back to a position at which the lock can be operated, and then advanced again after the spindle position indicator has been locked in position. The spindle position indicator can then be released once the valve has reached its extreme position, the indicator thus having been reset automatically without physical intervention by the user other than a simple manipulation of the valve lock key and rotation of the valve spindle.
The term xe2x80x9cslip clutchxe2x80x9d is used herein to mean any mechanical device which can be incorporated in the transmission so as to normally faithfully transmit rotation of the spindle to displacement of the position indicator but which enables relative slippage between them when the position indicator is locked and a sufficient torque is applied to the spindle.
The transmission may comprise a first sprocket driven by formations supported on the spindle engaging member and a second sprocket in driving engagement with the spindle position indicator, the slip clutch being located between the first and second sprockets such that the first sprocket can rotate relative to the second if sufficient torque is applied. The second sprocket may comprise two sets of axially spaced teeth and the spindle position indicator may comprise two axially spaced coaxial sprockets meshing with respective sets of teeth, actuation of the latch being prevented unless both the first and second spindle position indicator sprockets are in Determined rotational positions, the number of teeth in the sets of teeth and the number of teeth in the first and second spindle position indicator sprockets being selected to prevent actuation of the latch at more than one position of the spindle.
Preferably the housing is provided with a viewing window through which portions of the coaxial sprockets are visible, one or more of the sprockets carrying a marker to indicate when the sprockets are in the pre-determined rotational positions. The first and second spindle position indicator sprockets may define slots which are aligned with key displaceable members only when the sprockets are in the predetermined relative positions, the slots when so aligned permitting rotation of the key displaceable members, and rotation of the key displaceable members also causing actuation of the latch. The key displaceable members may be mounted to extend radially from a shaft which extends between two flanges in which the slots are defined, the shaft being rotatable about its major axis by the key. The shaft may bear against the latch and be shaped such that rotation of the shaft to a position in which the key displaceable members are engaged in the slots actuates the latch. The shaft may support an indicator which is visible when the shaft is rotated to the position in which the key displaceable members are engaged in the slots.
The slip clutch preferably comprises first and second members, surfaces of which are biased together by a spring, the surfaces being non-planar such that relative movement between them requires relative displacement between the two members and compression of the spring. The two surfaces may define mating peaks and troughs.
Preferably two spindle position indicators and two latches are arranged such that one latch when actuated prevents rotation of the spindle engaging member in one direction and the other latch when actuated prevents rotation of the spindle engaging member in the other direction, each spindle position indicator being coupled to the spindle engaging member by a respective transmission incorporating a respective slip clutch. This enables the valve lock to be secured at two spindle positions.
Preferably the spindle engaging member supports an annular array of teeth and the or each latch comprises a pivotal lever which is biased to a first position in which it engages the teeth and is moveable by the key to a second position in which it is spaced from the teeth, the lever being arranged such that when in the first position rotation of the teeth in one direction is permitted but rotation in the opposite direction is prevented as a result of the lever jamming an engagement with the teeth. A latch override member is preferably provided which may be driven into the housing to move the latch to the second position, means being provided to retain the driven member within the housing to indicate that the latch has been overridden.
Preferably the spindle engaging member defines a socket uniform, non-circular cross-section in planes perpendicular to an axis about which the spindle is rotatable, and the plurality of plates are engaged between the socket and spindle, each plate defining a peripheral edge which is shaped to fit the socket cross-section in each of the plurality of rotational positions relative to the spindle axis, and each plate defining an opening having a straight edge positioned relative to the plate to abut a plane surface defined by the spindle.
The present invention also provides a valve spindle adapter assembly comprising a housing which in use is mounted on a valve body from which extends a spindle that is rotatable relative to the valve body about a predetermined axis, a hub mounted on the housing so as to be rotatable about the spindle axis, and means for inter-engaging the hub and the spindle such that the hub and spindle rotate together, the spindle extending into a socket defined by the hub, and the socket being of uniform non-circular cross-section in planes perpendicular to the spindle axis, wherein the means for inter-engaging the hub and spindle comprises a plurality of plates each defining a peripheral edge which is shaped to fit the socket cross-section in each of a plurality of rotational positions relative to the spindle axis. each plate defining an opening having a straight edge positioned to abut said one planar surface of the spindle.
With such an adapter, a limited number of different plates with identical peripheral dimensions but different opening dimensions may be supplied to enable a fitter to interengage a standard valve lock hub with a wide range of different valve spindle configurations.